U.S. Pat. Nos. 4,278,622 and 4,279,843, issued on July 14, 1981 and July 21, 1981 to Nam P. Suh, describe a process that has become generally known as the "mixalloy process". Such process involves the mixing of materials in a molten, or slurry, state to form metallic mixtures by the direct impingement of the materials. While the patents describe such process in general terms, they do not provide details with respect to critical parameters that may be required to ensure completely homogeneous mixing, nor do they disclose specific information on any suitable techniques for using the process to cast the materials while preserving the homogeneous characteristics of the mixtures thereof.
Subsequent U.S. Pat. No. 4,706,730, issued on Nov. 17, 1987 to Luis E. Sanchez-Caldera et al., discloses a modification in the mixalloy process technique using an indirect impingement method. Such patent discloses that instabilities (i.e., variations of mixing quality) can be minimized, and even substantially eliminated, if, instead of using a head-on or direct collision or impingement of the impinging streams, the impingement angle is modified so as to induce oblique impingement. The term "instabilities" as used herein refers to variations of mixing quality due to changes, as a function of time, of the flow rates of the materials arriving at the mixing chamber.
It has been determined that, although such modification is necessary to prevent instabilities, the use of indirect impingement techniques does not always ensure a truly homogeneous mixing of the materials involved. For example, if the impinging streams include constituents that require a chemical reaction with each other upon mixing, it is possible that indirect impingement alone will not always provide adequate mixing to ensure that all the reactants will fully react with each other, even though stoichiometry is maintained locally.
Further, although the two earlier issued patents mentioned above also make reference to the need to cool the mixture rapidly enough to preserve the microstructure of the mixture, neither patent describes any specific techniques for actually carrying out the required cooling. Later issued U.S. Pat. No. 4,706,730, on the other hand, makes reference to cooling by making use of a mold or a die caster machine. Generally, the highest cooling rates achieved by the latter are only of the order of magnitude of about 100.degree. C./second (s.) and such a cooling rate may not be fast enough when processing certain types of metallic composites.
It is desirable to devise an appropriate method and system that ensures both a complete mixing of materials in a molten state and a sufficiently rapid cooling rate during the cooling thereof, i.e. , a cooling rate of greater than 100.degree. C./s.